This section is intended to provide a background or context to the invention that is, inter alia, recited in the claims. The description herein may include concepts that could be pursued, but are not necessarily ones that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, what is described in this section is not prior art to the description and claims in this application and is not admitted to be prior art by inclusion in this section.
A MCP is a type of solid state electron amplifier. The MCP can, for example, be used as a component in a detector system to detect low levels of electrons, ions, photons, or neutrons, and provide an amplified response via a plurality of secondary electron emissions that occur within the channels of the MCP. An MCP is comprised of an array of narrow pores in a flat plate that permeate from the front surface of the plate to the back surface of the plate. A high voltage is applied across the plate such that the back surface is typically at 1000 V higher potential than the front surface. An Electron enters the front of an MCP into a channel, and impinges on the channel wall causing secondary electron emissions to be produced by an emissive layer on the channel surface. These secondary electrons are accelerated towards the back of the plate by the high voltage bias and impact on the channel wall to produce additional secondary electrons resulting in a cascading increase in electrons along the length of the MCP channel that exit the opposite end of the channel. Since the MCP pores operate independently, a spatial pattern of electrons incident on the front surface will be preserved so that the back surface emits the same pattern but greatly amplified. In this way, the MCP can be used in imaging applications. Various detectors may be located downstream of the MCP to detect and record the exiting electrons. MCP detectors have numerous applications, including use in night vision technology, medical imaging devices, homeland security, and particle detectors for use in laboratories and high energy physics installations.
FIG. 1 depicts a configuration of a conventional MCP detector. MCPs may be prepared with various dimensions and shapes but often are circular and have a diameter of about 3 to 10 cm and a thickness on the order of about 1 mm. The MCP disc is generally fabricated from highly resistive glass by heating and drawing composite glass fiber bundles comprising a core glass material and a cladding glass material. The fiber bundles are then cut into thin discs and polished.
Wet chemical etching or other techniques are used to remove the core glass component from the composite glass fiber bundles resulting in the formation of the MCP pores. The MCP pores form a parallel array of straight, circular open channels with diameters typically of about 10 to 40 microns that extend through the disc from the front to the rear surface. The channel density of a MCP is typically between 104 and 106 channels per square centimeter.
Conventionally, the MCP is hydrogen fired, reducing lead oxide proximate the channel surfaces to semiconducting lead. The reduction process imparts a high electrical resistance between the front and rear of the plate. Functional MCPs typically have a resistance on the order of 106 to 108 Ohms, but this value may vary significantly depending on various process attributes. Finally, to complete the MCP, the front and rear surfaces of the MCP are metalized with thin conductive coatings of a material such as nichrome that serve as electrodes and provide electrical contact with the device.
A MCP fabricated using conventional processes suffer from several limitations. For example, the process does not allow for independent control over the resistance and secondary electron yield (SEY) characteristics of the MCP. Significantly, the resulting MCP is generally characterized by a negative temperature coefficient that causes the MCP to heat, leading to increased current, which further heats the plate, resulting in thermal runaway. Additionally, conventional fabrication processes are currently quite costly, with a 33 mm commercial diameter MCP costing on the order of $1,000.